Previous electronic lockbox systems that have had a portable electronic key to wirelessly communicate with the system lockboxes have required a constant battery drain at the lockbox itself, due to the requirement that the lockbox always be “listening” for a radio or light beam message that might be received at any time from the electronic key. Such lockbox systems accordingly tend to have a limited battery lifetime, and as such, the replacement of the lockbox batteries becomes a significant expense and a “nuisance” to the user, who must swap out the battery, or send the lockbox back to a dealer so that the dealer can swap out the battery. The more often a battery must be replaced, the more “down time” the user will experience per lockbox, and thus the greater the number of lockboxes that are needed by a user to maintain a specific number of operable lockboxes in the field.
In addition, previous electronic keys that have included a capability to wirelessly communicate directly with the system's central clearinghouse computer also tend to have a significant battery drain, especially those electronic keys that use cellular telephone systems as the communications link between the central computer and the electronic key. Although the batteries in the electronic keys might (typically) be rechargeable, it still can be an inconvenience for the user to have the key's battery go dead in the field, just when a lockbox is to be opened at a property site. Unless the user carries a spare (charged) battery, the user would not be able to use the electronic key to open the lockbox, thereby spoiling the showing of that property. In the conventional electronic lockbox systems, there is no backup plan to obtain access to the lockbox's secure compartment if the electronic key becomes inoperable.